The Omega Seamaster "Chronostop" single button sports chronograph model was introduced by Omega in 1967, and was designed for a younger, sportier clientele. The Chronostop won top prize at the Federation Horologer contest in 1966, in preparation for it's introduction at the Montreal World Exhibition in 1967. The Omega calibre 865 chronograph movement was developed specifically for the Chronostop, and features eccentric fine regulation and an ebauche from Lemania. The movement is featured on page 206 of Anton Kreuzer's reference book, "Omega Designs." This piece is the rarer "jumbo" sized Chronostop, and has the even rarer inner rotating 24-hour bezel (controlled by the crown at 10:00). Here's the details on this unusual one button Omega chronograph, which was produced for only a few years: OMEGA (SS Seamaster Jumbo "Chronostop" Chronograph) - Excellent 40mm signed stainless steel screwback case (reference 145.008) with dual signed crowns at 4:00 and 10:00, single chronograph push button at 2:00, signed 17 jewel calibre 865 chronograph movement (#270568xx), excellent original matte black "reverse pie-pan" dial with raised silver markers, white hands and arrow-tipped chronograph sweep seconds, signed original plastic crystal, signed original crowns at 4:00 and 10:00, 22mm generic black strap. The solid stainless steel screwback case on this vintage Chronostop is in excellent condition, and is signed Omega with the reference number 145.008 on the inner caseback, with crisp Seamonster logo and "Seamaster, Waterproof Tested 120m" engraved on the outer caseback. The signed 17 jewel calibre 865 chronograph movement is running fine, keeping excellent time, and the chronograph function works as designed, including crisply resetting of the chronograph seconds hand to zero. The matte black dial is original in excellent condition, and is signed, "Omega, Chronostop, Seamaster, T Swiss Made T." (Ignore the red color on the dial, which is a reflection of the shirt I was wearing at the time). The dial is unusual for it's "reverse pie-pan" design. The main functionality of this unique single-button chronograph is for timing events of very short duration. The chronograph seconds hand is engaged by the first pressing of the push button, and flys back to zero with the second pressing. The serial number on the movement places the date of production of this piece at 1969. This model sold for $2229 at [word removed] auction in 2007. UNUSUAL OVERSIZED 1969 VINTAGE OMEGA SS "CHRONOSTOP" SINGLE BUTTON SPORTS CHRONOGRAPH WITH INNER ROTATING 24-HOUR BEZEL AND ORIGINAL DIAL! Sell for $1195 plus shipping ($25 US Delivery or $60 International via Global Express).